CCNA Command Guide - Adam Vardy.pdf

8/17/2019 CCNA Command Guide - Adam Vardy.pdf

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CCNA Command Guide

Routing and Switching Command Guide with Examples


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Introduction

The CCNA Certification is a good foundation for other networking certificationsshould you may want to pursue in the future. Cisco Routers and Switches take upa huge chunk of the exam. The CCNA will test how much you know of Cisco

hardware and software.

CCNA Command Guide: Routing and Switching Command Guide with Examplesis designed to help you pass the CCNA Certification exam. The book is filled withthe following:

Illustrations: The book is filled with diagrams and pictures that will help youunderstand the concepts and functions of Cisco Routers and Switches.

Command Guides: Each chapter includes several command guides that will

help you improve your Routing and Switching Management skills.

Outlined Concepts: This book contains a good outline of topics, technicalterms and information. This should help you understand and remember termsthat are sure to come out in the certification exam.

While the main goal of this book is to help you pass the CCNA examination, mostof the information found in this book has practical applications that you will finduseful when performing your job as an IT professional.

This book is divided into two parts:

Part One: Routing with Cisco Routers

Part Two: Switching with Cisco Switches

At this point, you should understand that the concept of Routing and Switching is very similar except from the network layer they operate on. Most of the commandsare the same but the command protocols are different. Much of this will bediscussed in detail in the latter portions of each part.

Unlike other books that you can download from the internet, this book is very easy to use because of the special formatting it uses. Important concepts are in

boldface, italics or both. Since this is book is a command guide, the samplecommand lines that you can use to configure Cisco Routers and Switches arehighlighted by using a special font.


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Table of Contents

Introduction

Table of Contents

Part 1. Routing with CISCO Routers

Chapter 1. Layer 3 Routers

Layer 3 (Network Layer)

Functions of Layer 3 Router

Types of Protocol

Router FunctionsChapter 2. Router Management

Cisco Routers

Using the Cisco Routers

Local Connection

Configuring a CISCO Router

Cisco IOS Setup Mode Commands

Password Configuration

VTY Password

Setting-Up a Router Banners

Auxiliary Password

Privileged Password

Password Encryption

Recovering A Lost PasswordChapter 3. Network Routing

Types of Network Routes

Routing Protocols

Routed Protocols

Routing Methods

Chapter 4. Enhanced Interior Gateway Routing Protocol (EIGRP)

Characteristics of EIGRP

Components of EIGRP


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Routing Tables

EIGRP Packet Types

Convergence

Diffusing Update Algorithm (DUAL)

Classful vs. Classless Routing

Configuring EIGRP

Managing EIGRP Operation

Other EIGRP-related Terms

Chapter 5. Open Shortest Path First (OSPF) Protocol

Characteristics of OSPF

Convergence

Cost MetricOSPF Hierarchy

Selecting a Designated Router (DR)

Router ID (RID)

Configuring the OSPF

OSPF Protocol Configuration

Pertinent Commands

Part 2. Switching with CISCO Switches

Chapter 6. Layer 2 Switches

Hubs

Bridges

Switches

Hubs vs. Bridges vs. Switches

Switch Functions

Glossary of Terms (Switching)

Chapter 7. Switch Management

Handling Methods for Cisco Switches

Console Port

Auxiliary Ports

Chapter 8. Network Traffic ManagementSwitching Modes

Chapter 9. Spanning Tree Protocol (STP)


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Problems caused by Transmission Loops:

Spanning Tree Protocol

Assigning STP Port Types

Root Ports

Designated Ports

Choosing Designated Ports based on STP Path Cost

Choosing Designated Ports based on Bridge ID

STP Convergence

Bridge Protocol Data Units (BPDUs)

STP Port States

Exclusive Cisco STP Options

Chapter 10. Virtual Local Area Network (VLAN)Benefits of VLANs

Creating VLANs

Kinds of VLAN

VLAN Trunking

EtherChannel

Configuring EtherChannel

Types of Switch Ports

Chapter 11. Voice over IP (VoIP)

Quality of Service (QOS)

Cisco IP Phone

Cisco Discovery Protocol (CDP)

Enabling QoS in the Upstream Switch

Chapter 12. Troubleshooting Switches

Gathering Information

Troubleshooting Switch Connectivity

Conclusion


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Part 1

Routing with CISCO Routers


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Chapter 1. Layer 3 Routers

The network layer in both TCP/IP and Open Systems Interconnection network

models is called Layer 3. Network layer protocols and devices are in charge of transferring data that are stored in packets from one host to another. This methodof data transfer is called routing. These hosts can be adjacent to each other butthey can also be several miles apart.

The difference between Layer 2 (discussed in Part 3, Chapter 14) and Layer 3 isthat the former routes data packets between devices that belong to the same LAN while the latter routes data frames between devices that belong to different LAN.This is where Layer 2 got is name, data link layer.


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Layer 3 (Network Layer)

Logical addresses or more popularly known as IP addresses are assigned by Network Layer to all the devices connected to the network. These addresses areused to identify hosts (source and destination) and the specific network wheredata packets are being routed. Take note that IP addresses or logical addresses are

assigned to network protocols and not to physical devices (modem, network card).For physical devices, physical addresses are assigned.

The functions of network layer include:

. Acceptance of data pieces transported from transitions layer within the transferhost.

. Assembling of data pieces into data packets. In each data packet, the network layer writes IP addresses of source and destination hosts for tracking.

. Directing the data packets to the specific data link layer. The data link layer(Layer 2) will then send the data packets through the LAN connection.

Once the data packets have been sent to Layer 2, it will then perform the followingfunctions:

. Acceptance of data packets from the network layer.

. Assembling of the data pieces, stored in data packets, in a data frame. Layer 2 writes the physical MAC addresses of the source and destination hosts of the

device in each assembled data frame.

. Directing the data frame to the physical device displaying the correct physicalMAC address. The device then decodes the data frame to readable optical orelectrical signal.


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Functions of Layer 3 Router

The Layer 2 switch is designed to oversee the creation of a single impact domainper port and the forwarding of data frames on exit transfer ports that managed toget to the frame’s destination.

Using the snail mail analogy, Layer 2 switch acts as the mailman who delivers the

mail to specific addresses inscribed in the envelope. Routers act as the local postoffice that organizes the letters by street before it hands the mail to the mailman.

Routers are usually slower than their Layer 2 counterpart is. This is becauserouters have to first check for data packets within the network layer whereas Layer2 only checks datalink frames to check for the physical address of each datapacket.

Network Layers (comp4net.com)

The above figure shows how data packets are sent, processed and read by anintermediary device. In this case, the intermediary device is a router. The flow of the data packets from source to destination hosts (sender to receiver) in the figuredescribes how data is being processed by two different LANs. The router inspectsthe data packets first in the network layer before it sends it to the data-link framelayer in the form of data frames. These data frames are then sent to specificphysical devices.

While the main function of the router is to transfer data packets through the

source and destination hosts of each network, it is also responsible for:

. Inspection of the IP written in each passing data packet.


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. Extraction of the logical IP address of the destination host.

. Inspection of the extracted IP address to decode the network where the datapacket must be sent.

. Sending of the data packet to the correct destination network. (This is if therouter recognizes the destination network.)

If the router is unable to recognize the destination network, it will just transfer thedata packet to its own exit gateway for outbound transfer.


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Types of Protocol

At the network layer, there are two types of recognized protocols: routingrotocols and routed protocols.

. Routing Protocols: These protocols are used to transfer route updatepackets from one host to another. Information about new routes and new

networks are stored within the route update packets. These packets are sent by routers to each other whenever a new route is opened or a new network isestablished.

Among the more prominent routing protocols are Routing InformationProtocol (RIP; Chapter 11), Enhanced Interior Gateway Routing Protocol(EIGRP; Chapter 12), and Open Shortest Path First (OSPF) Protocol(Chapter 13).

These routing protocols employ varying systematic metrics to determine which routes and networks are better compared to others.

2. Routed Protocols: These protocols are used to transfer data packets as wellas to identify hosts from networks in the global environment. Routed protocolsassign a unique logical address for each host in the network.

Good examples of routed protocols are AppleTalk, SNA, IPX and IPv6.


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Router Functions

The four basic functions performed by a Layer 3 router are:

. Maintaining routing protocols;

. Establishing routing tables by means of routing protocols;

. Keeping tab of routing tables; and

. Routing data packets.

Keep in mind that logical IP address follows a hierarchy. They have numbers thatcorrespond to the name of the network and numbers that correspond to the hostdevice.

Consider the IP address of the network is 192.168.45.0 for example. Hosts withinthe network must have an IP address that begins with 192.168.45. Consequently,hosts within the network described by an IP address 192.168.62.0 should havehosts whose IP address begins with 192.168.62. In the two examples, the firstthree numbers are used to identify the network while the last number is used toidentify the host.

Routing Protocols

Before two networks are able to send data packets to and from each other, therouters need to set up a consistent routing protocol. The different stages of setting

up a consistent routing protocol are:. Setting up the routing protocol for each router;

. Accessing the interface of each router; and

. Customizing the options for routing protocols.

Unless the router is programmed to negotiate routing protocols with each other, you have to execute each stage to manage routing protocols.

Routing Tables

While routing protocols contain specific instructions on how the router shouldexchange information in forms of data packets within networks, routing tablesmanage the changes within the network, the paths for each network and themetrics for each path. Aside from that, routing tables also keep track of thefollowing:

. List of networks remembered and forgotten by each router

. Data stored within the router interface

. Metrics related to each path.


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Chapter 2. Router Management

The Cisco Internetwork Operating System (Cisco IOS) is responsible for managingCisco routers. Managing Cisco routers and managing Cisco switches is similar. For both routers and switches, only the output differs — the IOS commands are very

similar. In fact, the graphical user interface used for managing both Cisco routersand switches is the same except for some differences. For instance, Cisco Routerand Security Device Manager (SDM) is obviously only available for Cisco Routers(and not for Cisco Switches.)


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Cisco Routers

The three classifications of Cisco Routers are as follows:

Cisco Router Best Suited for

Entry-level Router Access Layer and DistributionLayer

Midrange Router Access Layer and DistributionLayer

Top-of-the-line Router Core Layer and DistributionLayer

Top-of-the-line Cisco routers are designed to perform the following the routers intheir respective networks:

WAN gateway connectivity

Inter-VLAN routing

Open Shortest Path Fist (OSPF) backup designated router (BDR)

OPSF designated router (DR)


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Using the Cisco Routers

Like almost all router brands, Cisco does not allow user interaction, at least notdirectly. Managing the controls of a Cisco router can be done by connecting it to acomputer host either remotely or locally. Once the router is connected to thecomputer host, users can now open the user interface in the computer host to

engage with the Cisco Router.

ocal Connection

A typical cisco router has several ports that where line plugs can be insertedto connect to the host computer or other similar network-enabled devices.

Other ports, typically bearing different colors from the rest, serve otherfunctions other than ensuring connectivity to network layers. These portsare:

Auxiliary Port

This port is used to connect a router to the main computer frame by means of a rollover cable. The modem connected to the auxiliary port of the router is connected via a telephone line to a similar modem that isconnected to the main computer frame.

In theory, auxiliary ports are really designed with remote connections.The only difference is that setting up remote connections with the aid of auxiliary port requires a modem to be locally connected to the router viathe auxiliary port.

Auxiliary ports (cisco.com)

Console Port

Similar to Auxiliary Ports, Console ports are designed to connect main

computer frame to router through a rollover cable. This port is used tolink the router to the console locally.

The Cisco Operating System has a console facility that aids user


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interaction through prompts, status updates, error warnings, anddiagnostic messages. The console facility can be accessed by connectingthe router through its console port to the computer host using rollovercables.

After connecting the computer to the router using a physical connection,the terminal emulation program must be accessed in the computer toopen the terminal setting in the router. Examples of terminal emulationprograms are:

HyperTerminal

SecureCRT

TeraTerm

Remote Connection

Using a remote management computer host, CISCO’s terminal window androuter console can be accessed remotely. Remote access to CISCO routerscan be set up using:

Console Terminal Server can be used to determine the IP address of theconsole. In fact, Console Terminal Servers can be programmed to assign routerconsole facility to specific TCP/IP port serial as well as specific IP addresses inthe network. Using any of the terminal emulation programs,

IP:port can be

connected to the Console Terminal Server.

Telnet Applications can also be used to access the router’s network IP address.The router is already assigned with a specific network IP address, which assiststhe network to detect the router.

Auxiliary Ports, as explained in the previous section, can be used to connectthe router to the remote management computer host.

Configuring a CISCO Router

If you don’t understand how to configure a CISCO router, it is unlikely that you’llpass the CCNA certification exam. Aside from just getting the CISCO routerhooked up, this section will also teach you how to deal with startup and runningstructure controls.

CISCO routers always come with the following items:

AC power cord

Rollover Cable

Mounting Brackets


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Router and Security Device Manager CD

Router Documentation CD

Freshly unboxed Cisco routers are not yet configured with any setting. The lack of a startup configuration requires you to create one. When no startup configurationsettings are stored within the NVRAM, Cisco Routes return to setup mode inpreparation for initial router configuration. This happens when the:

device is being used for the first time; or when

initial router configuration has been wiped off.

The two ways to build the initial configuration of a new Cisco Router are:

Connecting to Cisco IOS setup mode commands

Accessing the Initial Configuration Dialog Box

Cisco IOS Setup Mode Commands

1. Naming the Router

In the Cisco IOS command, you can specify a name for the router using ahostname. To name the router, just run the following code:

Router>en

Router #config t

Router(config) #hostname SampleName

RT01(config)#exit

RT01 #disable

RT01>

2. Setting up the management IP address configuration

The Cisco IOS commands ip default-gateway and ip address, you

can now establish the IP gateway and IP address of the router. This lets youuse HTTP or Telnet to establish a connection to the router from distantlocations.

To customize the current default gateway and management IP address on

the router, you can implement the following commands:Router>en

Router #config t


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Router(config) #int fe0/0

RT01(config) #ip default0gateway 192.168.72.2

RT01(config) #exit

RT01(config-if) #ip address 192.168.72.30255.255.255.255.0

RT01(config-if) #no shutdown

RT01(config-if) #exit

RT01 #disable

RT01>

The first two lines:

Router>en

Router #config t

can be used interchangeably with:

Router>enable

Router #configure terminal

These two lines enable the privileged global configuration mode in the CiscoIOS. This configuration mode allows you to implement commands that cantweak the settings of the global router or simply the settings of the entirerouter.

This line:

Router(config) #int fe0/0

can be used interchangeably with:

Router(config) #interface fastethernet0/0

This command allows you to choose which command interface to work on.

In the example provided in the previous page, this line:RT1(config-if) #ip address 192.168.72.30255.255.255.255.0


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Cisco features routers that supply information to the network and the devices on it based on the kind of access enabled by a specific password. Cisco routers allow four kinds of access:

Console Password This password grants access to theRouter console via the Console Terminal

Server or the console port.

Auxiliary Password

This password grants access to theRouter console via the auxiliary port inthe router.

VTY Lines Password

This password grants access to Telnetand Security Shell (SSH) to the VirtualType Terminal (VTY). The VTY is called

such because it does not require any physical connection from the terminal tothe router. This remote connection usesthe IP address of the router to connectthe computer host directly to thenetwork.

Privileged

Password

This password grants access for select

users who have a security clearance thatallows them to configure the operation of the management computer host. Theseusers are able to implement special IOScommand.

By default, both the auxiliary port and console port are enabled regardless if apassword is a configured for each of them. This poses a security vulnerability tothe router network thus Cisco recommends that, at the very least, a consolepassword must be configured.

Also by default, the VTY lines are disabled. Enabling VTY require theconfiguration of VTY password. To set the password for the Cisco router, the CiscoIOS interface can be instructed to prepare the router for authentication. In the IOSinterface, implement the following commands to set the console password:

router001 > en

router001 #configure trouter001 (config)#line cons 0)

router001 (config-line) #password x1dmv4


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router001 (config-line) #login

router001 (config-line) #exit

router001 (config) #exit

router001 #disable

router001 >

These lines can be used interchangeably:

router001 > en

router001 > enable

The same goes for this line:

router001 #config t

router001 #configure terminal

These two lines enable the privileged global configuration mode in the Cisco IOS.This configuration mode allows you to implement commands that can tweak thesettings of the global router or simply the settings of the entire router. Also:

line console0

This IOS command chooses the consoleline. All Cisco devices (routers or routers)only have one kind of console line:console 0

Passwordx1dmv4

This IOS command sets the password tox1dmv4 on the access line of the console.

VTY Password

The following commands can be implemented in the Cisco IOS interface:

router001 > en

router001 #config t

router001 (config) #line vty 0 ?

14 last line number

router001 (config-line) #line vty 0-12


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router001 (config-line) #password newx1dmv4




router001 #disable

router001 >

To have a good understanding of how each block of line is used:

#line vty 0 ? This command poses a query that determines the number of VTY lines free.

0-12 last linenumber

This is the response of theCisco IOS saying that lines 0 to12 (or 13 lines) available for therouter. This means there areexactly 13 Telnet sessions thatcan be simultaneously openedfor this router.

#line vty 0-15 This command selects all the 0-12 VTY access lines available.Older versions of Cisco routersonly use four VTY lines butnewer implementations have atleast 1,180 VTY lines. This is why the previous commandshad to pose first an inquiry onhow many VTY lines areavailable.

#passwordnewx1dmv4

This IOS command sets thepassword to x1dmv4 on the

VTY lines chosen in theprevious command line.

Cisco devices have several VTY access lines because of two major reasons:

. Several VTY access lines allow multiple users to manage the router:Large router networks grants access to more than one router manager. By


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using SSH or Telnet, router managers can access the router through remoteconnection.

. A VTY access line allows a user to connect to a different device alsoconnected to the router. In this case, two VTY lines are required. One thatconnects the computer unit to the router and another that connects the routerto the other device.


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etting-Up a Router Banners

Router banners are brief messages that the router display to a terminal connectedto it. This is common with routers that are being accessed by multiple computerterminals. It can even display which router a user is using including the

configuration limits and connection guidelines.Companies and organizations can also configure a security warning in the bannermessage to ward off potential unauthorized access to the router. This gives acompany to exercise legal action should an illegal access be detected by thesystem.

The four different types of banners that Cisco routers can display are:

. EXEC process creation banner: This type of banner is configured in thescreen during the creation of EXEC processes.

. Message of the Day (MOTD) banner: This banner displays a messageevery time a user establishes a connection with the router. Regardless if theconnection is remote or local, the router will display this message when there isan attempt to log into the router network. The MOTD banner is usually used to ward off users attempting an illegal connection to the router.

. Incoming terminal connection banner: This banner is often displayedafter the MOTD banner. This banner is used to give additional information for

users who are connecting using VTY or reverse TTY computer terminals.

. Login banner: This banner is displayed to give information to the usersabout the router. This may also contain additional guidelines on how theconnection should be used.


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The following command can be implemented to setup an MOTD banner on every router connection:

router001 > en

router001 #config t

router001 (config) #banner motd /

Enter TEXT message. End with character ‘-’.

$This router is owned by example.com. Should the systemdetect any unauthorized access to the router network,the security system will trace the user login to display

security credentials from access point. If you are notfrom example.com, nor a client nor a business partner,please disconnect immediately.

-

router001 (config)#

The command #banner motd / opens the text editor interface. The delimiting

character set in this command is ”/”, which means that the IOS interface will

process the text input only until it detects a ”/.”

The delimiting character can be any character that could not be found on the textof the MOTD banner.

esetting a Cisco Router

Whenever the router detects that there is no initial configuration activated in theNVRAM, it automatically implements Express Setup mode. This happens whenthe router has just been brought out of its box or if the initial configuration has

been deleted from the NVRAM.Relieving the Cisco router of its current configuration is usually a last-resorttroubleshooting attempt to fix connection problems. After the router is reset, thefollowing information will also lose their configured value:

IP address

Telnet password

Host name

Console password

Subnet mask


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Default gateway

To reset the settings of the router and delete any configuration stored in theNVRAM:

. Press the Mode button and held it for a few seconds. Hold the Mode buttonuntil the LED indicators in the router begin blinking.

. Wait for the LED indicators to stop blinking before you stop holding the Mode button. After all the LED has stopped blinking, the router should reboot by itself.

. Release the Mode button

The Cisco bootstrap program allows router managers to tweak the bootingprocedure of any Cisco router connected to the computer host. The boot commanddoes the following:

Manage the loaded Cisco IOS image file

Enable the Ctrl + Break system key while the router is booting

Select which initial configuration should be used

Enable manual booting

Format the size of the NVRAM.

The following command block instructs the IOS interface to show the availableoptions for the boot command:

router001 >

router001 >en

Password: x1dmv4

router001 #config t

router001 (config) #

router001 (config) #boot ?

system

System Image

manual

Manual Boot

boothlpr

boots the Helper System Image


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The following are the global configuration settings that can be executed using the boot command:

booth1pr While this is not usually touched uponin the CCNA test, this command

accesses the image file that helps the boot system.

buffersize This allows the user to determine thememory size of the NVRAM. Should theuser desire to add extra Cisco IOSimages to the flash memory, the size of the NVRA must be increased.

config-file This allows the user to determine theparticular configuration file that should be using as the router boots up. This isused whenever the user needs to check on other alternatives to the initialconfiguration file.

enable-break If this option is enabled, the user can

disrupt the booting process by pressingCtrl + Break shortcut keys.

helper These options are also not included inthe coverage of the CCNA test.

helper-config-file

manual This option allows the user to boot the

router manually without impairing thesystem nor any configuration setting inplace.

private-config-file

This option allows the user to determinethe private configuration file that could be loaded while the router is booting up.

Private configuration files are designed

to safeguard highly-securedconfiguration information likeencryption keys for SSH.


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system This option allows the user to load aspecific image file in the IOS interfacefor checking.


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NVRAM/Config file

buffer size: 62642

router001 #disable

router001 >

The show boot command displays the current settings of the boot resources of therouter.


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Cisco Router File Systems

The three main directories that are used by the Cisco router are:

Nvram This is where private-config and startup-

config is stored.

System This directory that is found in the RAM is where therunning-config file is stored.

Flash This directory refers to the flash memory. This wherethe Cisco IOS system image, which the bootstrapprogram loads, during the system boot process.

uxiliary Password

Most Cisco routers have auxiliary ports. These ports can be protected by integrating a password specifically for auxiliary ports. To setup a password forauxiliary ports, the following command lines can be implemented in the system:

router001 > en

router001 #config trouter001 (config) #line aux 0

router001 (config-line) #password aux1dan4




router001 #disable

router001 >

These two lines can be used interchangeably:

router001 > en

router001 > enable

The same goes for this line:

router001 #config t

router001 #conf ter

router001 #configure terminal


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These two lines enable the privileged global configuration mode in the Cisco IOS.This configuration mode allows you to implement commands that can tweak thesettings of the global router or simply the settings of the entire router. Also:

line aux 0 This IOS command chooses theauxiliary line. All Cisco devices (routersor routers) only have one kind of auxiliary line: aux 0

passwordaux1dmv4

This IOS command sets the password toaux1dmv4 on the access line of the

console.

rivileged Password

There are IOS commands that should only be configured by specific users as thesecommands are crucial to the overall functionality of the router. The twocommands used to setup a privileged password are:

enable passwordprivx1dan14

This command sets the stringprivx1dan14 as the privileged

password. In other words, beforea user can access the functionsthat are restricted for privilegedusers, they must key inprivx1dan14 in the IOS

interface.

enable secretcryptx1dan14

This command setscryptx1dan14 as the privileged

password. Compared to thecommand line above, thispassword is encrypted. Alsounlike the above command line,this command is supported only

by newer IOS interfaces that arecompatible with the newerimplementations of Ciscorouters.


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Before you set the privileged password, you must first enable this option by keyingin the following commands:

enablepassword

This enables password protection foradministrative privileges. The password isstored in an unencrypted format.

enable secret The same as the above command line exceptfrom the fact that the password is stored in anencrypted format.

Privileged passwords are stored in a server called Terminal Access Controllerccess Control Sytem (TACACS). This server is often used by larger networks

composed of multiple routers that allow the administrators to configure the

privileged password only once for all routers in the network as opposed to settingup the passwords on each of the routers.

router001 > en

router001 # config t)

router001 (config) #enable secret cryptx1dan14


router001 #disable

router001 >

assword Encryption

Passwords are saved in plain text format by default in the startup configurationfile in NVRAM and running configuration in the RAM. By implementing the show

start-up config command and the show running-config command, the

passwords will be displayed in simple text. This poses a security risk especially if the routers hold confidential data resources in the system. This is why it is advised

that passwords must be encrypted in the system.

Other passwords like theconsole password, auxiliary password, and VTY passwordare not encrypted regardless if the command enable secret is used to

configure any of the three passwords. To encrypt these passwords, the service

password-encryption command must be used. Consider the command block

below:

router001 > en

router001 #config t

router001 (config) #service password-encryption



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router001 #disable

router001 >

ecovering A Lost Password

Password can only be recovered if the password-recovery feature is enabled in

the system before the password is lost. This can be done while the routerundergoes the boot process. To recover the lost password, the following stepsmust be followed:

. Using any of the methods enumerated in one of the previous sections in thischapter, interrupt the regular boot process.

. Access the flash file system manually.

. Prevent the Cisco IOS interface from accessing the startup configuration file by hiding it.

. Start the router manually until the IOS has finished loading in the RAM.

. Reactivate the startup configuration file.

. Transfer the configuration file to RAM from NVRAM.

. Change the password.

. Store the running configuration.

. Reset the boot process to its original settings.

0. Restart the router.

Chapter 3. Network Routing

The main role of routers is to transmit data packets from one network to another. Aside from this, the routers are responsible for the following:

Transmit packages based on routing tables and routing protocols

Maintain routing protocols

Organize routing information into routing tables

Manage routing tables

Data transmission paths that extend through different networks are called a


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network route. Each route joins two end nodes, each representing a network device that is capable of being assigned with IP address. Examples of which aresmart phones, tablets, gaming consoles, camera interface, and computer hosts.

It is possible to have more than one route in between nodes. This is because the

router employs a special algorithm that computes for the best route available before a data packet is sent from one point (source) to another (destination). Thealgorithm takes into consideration route metrics, which include the cost of theresources, and the time it takes to send the data packets.

Within the data transmission path, there should at least be two routers positionedanywhere in between the source and destination nodes. For example, whensending a message via a chat module installed in your computer, the computer

sends packets of data containing the message you intend to send to a computeruser elsewhere. These data packets pass through the home router. The homerouter then transmits these data packets to the Internet Service provider (ISP) viathe outbound gateway. The Internet Service Provider’s outbound gateway thentransmits the packets through cables and cables of integrated network chain untilit reaches the network/ server of the recipient user. Data packets will be received by the router of the receiving host computer at lightning speed. Notice that,depending on the location of the recipient, data packets traveled through at leastfour routers:

Home router of the sender

Outbound Gateway (ISP) of the sender

Inbound Gateway (ISP) of the recipient

Home router of the recipient


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Types of Network Routes

There are three types of network routes namely:

. Static routes

Perfect for smaller networks, such as home networks, static routes are routesthat are manually configured on the router. Aside from home networks, LANconnections can also be managed by static routes because these connectionsseldom change. If for any reason the connection changed, the router must bemanually configured to indicate the new transmission paths.

Static routes are useful to home and LAN connections because of thefollowing:

. Efficient Routing: Routing protocols are disabled whenever static routes areconfigured. Since routing protocols use bandwidth, static routes save bandwidth consumption. On the flipside, routing protocols are enabled whenever dynamic routing procedures are used. Routing protocols use bandwidth because update packets are being sent between two routers.

b. Security: Configuring static routes allows the user to manage thetransmission paths used when sending data packets. This is useful for routersthat have been transmitting highly-critical and highly-confidential information.Regularly updating static routes provide an extra layer of information security and foil any attempts to hack into the network system and phish for data. Also:

Firewalls can be introduced to static routes to filter routing data within thenetwork border.

Regardless of the route, Virtual Private Networking (VPN) safeguards the datasending mechanism regardless of the route where the data travels.

In other words, security risks can be managed by building a firewall or by using VPN.


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However, while static routes have many upsides, they also have a few downsides like:


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a. Management Overhead: Maintenance can be tricky because every time the data transmission paths change, the router configuration must beupdated.

b. Scalability: Static routes are impractical when managing largernetworks. Wide-scale networks are composed of thousands of routes toreach other areas of the network. A good example of these networks iscommercial internet connections provided by the Internet ServiceProvider. Houses are connected to a single network managed by a server.Even so, it is impractical (and almost impossible) to configure all theroutes to be static. Also, should any of the routes change, all the staticroutes in the network must also be changed. This is the reason why staticnetworks are perfect only for small-scale networks.

c. Accuracy: If the network routes change and no configurations weremade on the static network, the router will not have an accurateunderstanding of the network. As a result, data transmissions are eitherdelayed or lost completely.

Static routes can be configured by using the Cisco interface by enteringthe following command:

ip route dest-ip subnet {next-hop_ip | interface}

2. Default routes

Whenever data packets are sent to a new destination network, packets follow a different kind of static routes. New destination networks are not likely tohave an entry in the routing tables so a new route is assigned to them. Thisroute is called default routes. It is not uncommon for a router to receive adata packet addressed to a new network that it has no information of; in thiscase, the router transmits the data packet through the default route.

Network managers always make sure that a default route is configured in therouter in case data packets addressed to newer unrecognized networks is


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received by the default outbound gateway. Default routes transmit datapackets via the default gateway configured in the network.

Configuring default routes

Configuring default routes is similar to configuring a regular route using theglobal configuration mode. By using Cisco IOS interface, default routes can be configured manually by following the examples provided below:

Assuming that both the subnet mask and the IP address of the destinationnetwork are 255.255.255.255, run the code below to configure the default

route:

RT10-1> en

RT10-1 #config t

RT10-1 (config) #ip route 255.255.255.255255.255.255.255 serial 0/0

RT10-1 (config) #exit

RT10-1 #disableRT10-1>

3. Dynamic routes

These routes change on a regular basis. The dynamics of dynamic routes are being managed by routing protocols. They are responsible for updating

router configuration whenever changes such as the following happen:

Link-state landscape

Available bandwidth

Updates in network traffic

Updates in network topology

Using dynamic routes have the following advantages:


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a. Low maintenance: Unlike static routes that require constantly updating therouting configuration whenever the network landscape changes, dynamicroutes require no such laborious task. Dynamic routing immediately recognizeschanges in data transmission paths. In response, router settings areimmediately configured to complement changes in the network. This task ismanaged by routing protocols who exchange information with other routers ona regular basis.

b. Accuracy: Dynamic routes use routing protocols to gather information aboutother routers. This exchange of information between routers is done by sending back and forth update packets so the routing protocols can immediately configure router settings.

c. Scalability: Unlike static routes that are best-suited for smaller networks,dynamic networks are perfect for larger networks. Routing protocols managehundreds or possibly thousands of routes in large-scale networks. This seemsto be a logistical nightmare for static routes. For dynamic routes however, thisis just another day in the office. Routing protocols minimizemiscommunication among routers by constantly communicating with routes within their network

Dynamic routes only have one known disadvantage: network overheads.Since routing protocols facilitate a constant exchange of information withother routers, dynamic routes consume more bandwidth causing network overheads.


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Routing Protocols

The main function of routing protocols is to exchange routes, network and metric

information in forms of data packets to determine the best route available. Thisinformation is used to build a routing table that contains all the pertinentinformation about routes and the corresponding metrics associated to it.

There are several routing protocols but you only need to know three of them:

Routing Information Protocol (RIP)

Enhanced Interior Gateway Routing Protocol (EIGRP); and

Open Shortest Path First (OSPF)


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Routed Protocols

The source and destination address of each data packet is assigned by routed rotocol . The address tagged in the data packet is a unique combination of

numbers that correspond to the address of the source and destination node. Themost commonly-used routed protocols are:

Novell Netware Internetwork Packet Exchange (IPX)

AppleTalk

Internet Protocol ver. 4 (IPv4)

Internet Protocol ver. 6 (IPv6)

Depending on the results of the evaluations made by the routing protocol, therouters choose a destination for a data packet based on decision criteria. Routingtables build an inventory list of all the networks, paths, routes and metricsassociated with all the nodes it has touched bases with before. Decisions made by the routing protocols are based on the information stored in the routing table.

Routing protocols base their decisions on two aspects:

. Administrative/Virtual distance: This aspect measures the reliability of the information integrated in the data packets about the destination node.Routers gather information about the network routes through the following:

Direct connection to the network: Routers do not use intermediaries to gatherinformation about the routes. Updates in the form of data packet are sent to

different routers for information-gathering purpose.

Indirect connection to the network (via other routers): Pieces of informationabout other network not within range are gathered from what informationother routers have gathered.

Static Route connection to the network: The router is not directly in touch witha network but it is informed of its existence by the static route.

Routers compute for the reliability of the information based on the source.It follows a hierarchy that favors routers nearest it. Cisco measures


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administrative distance by assigning distance values:

Source of

Information

Administrative Distance Values

Direct Connection

0

Static route

1

Internal EIGRP

90

OSPF

110

RIP (ver. 1 and ver. 2)

120

External EIGRP

170

Routers prefer information with lower administrative distance values.

2. Routing Protocol Metrics: This computes the costs associated with eachroute. Examples of weighted costs are as follows: link state, available bandwidth and traffic.

The various routing protocol differs on how they calculate the efficiency of each of the router hence it is understandable that each of the routingprotocols may have different preferred routes compared to the rest. Whenrouting protocols disagree with each other, routers select the best route by

computing for administrative distances instead.

Here are some of the metrics used in route selection:


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. Bandwidth: This refers to the capacity of information that can be held by aroute to reach the destination. Bandwidth is measured in terms of bits persecond (bps). Routes with higher bandwidth are preferred by most routingprotocols because data packets tend to reach the destination point faster with alarger bandwidth. This metric is given more weight by EIGRP.

b. Hop Count: This refers to the number of routers between the source nodeand the destination node. Router protocols tend to pick routes with less hopcounts to minimize delay. RIP is notorious for using this metric on determining which route to pick.

c. Cost: This refers to the value computed based on the bandwidth of a network route. The figure is measure by 108 / bandwidth. OSPF uses this route moreheavily than it does other routing protocol metric.

d. Maximum Transmission Unit (MTU): This refers to the size of each datapacket. MTU is measured in terms of bytes. The bigger the size, the bigger theamount of data that can be transferred at any given time. EIGRP uses MTUheavily, preferring higher MTU values.

e. Load: This refers to the bandwidth presently consumed by the data traffic atany given route. It is computed by getting the difference between the availableunused bandwidth and the total bandwidth of the route. EIGRP picks network routes with lower load.

f. Reliability: This refers to the how much time is available in a specific route.

EIGRP selects route with higher reliability values.

g. Delay: This refers to the average amount of time a data packet takes to reachthe destination host. This is compute based on the following metric:

Propagation delay: This refers to the time taken by the signal to spreadthroughout all the transmission paths.

Transmission delay: This refers to the time taken by data packets in betweenhops.


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Queuing delay: This refers to the time a packet spends in queue before it isreleased to an outbound port.

Processing delay: This refers to the time spend by the router to inspect the

encoded destination address.


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Routing Methods

Routers use the different standards through which routing protocols compute for

the most viable route. Before they even measure the efficiency of each route,routing protocols initiate a progressive trade of information between routers to build a reliable routing table. This exchange of information is done through many different methods. These are:

. Distance Vector Routing: Routers, who are using protocols that measuredistance between nodes, complete their routing table by the information takenfrom their own direct connection and from neighboring routers.

This is a routing procedure where routers trust the information sent to them by neighbor routers. The information sent by neighbor routers is also sent toa different neighbor router who might not have direct connection with theoriginal router that sent the information. Rumor routing is another name fordistance routing.

Distance vector routing employs the following special mechanisms to avoidincurring routing loops:

Triggered update: This feature lets different routers share updates with eachother once a router becomes functional or when something has changed withinthe network.

Poison reverse: This feature sends a message to all neighbor routers that aspecific network is down and therefore must not be used as a route for a datapacket.

Split horizon: This feature hinders the promotion of the route back to itsoriginal promoter.

Hold-down timer: This feature hinders the acceptance of new updates onspecific routes for a preset period if the route is deemed unavailable. Thisprevents the re-advertisement of routes that are not functional as this may


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eventually lead to routing loops.

Route poisoning: Similar to poison reverse, this feature sets the number of hops to the maximum number of hops plus 1. This automatically givesneighboring routers information that such route is no longer reachable.

Maximum hop count: This feature makes sure that the data packet does notfollow a route that requires more hops than the predetermined maximum hopcount.

Routing

Protocol

Maximum

Hop Count

RIP 15

OSPF 255 (subject to userconfiguration)

EIGRP Unlimited

Routing loops eventually lead to a route failing. This often takes time beforeall the concerned routers are informed.

The two protocols that use distance vector routing procedures are RIP and

IGRP (not to be confused with EIGRP).

2. Link-State Routing: Routing protocols that follow link-state routingprocedures build routing tables using information exclusively from the updatesgathered from neighbor routers. Instead of just pooling the information foundin the neighbor’s routing table, link-state protocol gets a good view of thenetwork topology and routes within and beyond neighboring routers.

Link-state protocols are characterized by the following:


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Compared to distance vector protocol that sends and receives route updates ona regular basis, link-state protocol only sends and receives update when changehas been detected in any of the immediate routes.

Aside from routing tables, link-state protocol also manages topology and

neighbor tables.

Updates send by neighbor routers only contain information about routes thechanged.

Routers under link-state protocols exchange “hello” packets to get a goodunderstanding of neighbor routers.

Link-state routing is prominently configured in the Open Shortest Path First (OSPF).

3. Hybrid Routing

Protocols that employ hybrid routing combines the properties of both link-state and distance vectors including:

Similar with distance vector protocols, hybrid routing protocols useadministrative distance metric to determine route quality.

Similar with link-state protocols, hybrid routing protocols use MTU, load,reliability, delay and available bandwidth to determine route quality.

Cisco-proprietary Enhance IGRP (EIGRP) uses hybrid routing procedures.

Convergence: This refers to the first exchange of information made by therouters to each other as they attempt to connect to the network.


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Chapter 4. Enhanced Interior Gateway RoutingProtocol (EIGRP)

Unique to Cisco routers, Enhanced Interior Gateway Routing Protocol (EIGRP)has plenty of upsides compared to that of the Interior Gateway Routing Protocol(IGRP) and its successor Routing Information Protocol (RIP). Both IGRP andEIGRP are known to be a distance vector protocol. The only difference is that thelatter of the two has a better set of distance vector and response algorithm. Thisalgorithm is responsible for determining the best data path towards a particulardestination. Also, it employs an advanced loop mitigation system compared tothat of both IGRP and RIP making it perfect for link-state protocols.

Aside from the ones mentioned above, Cisco designed EIGRP to supersede IGRP’slimitations. Compared to IGRP and RIP, EIGRP:

Supports both VLSM and CIDR

Congregates quickly

Has a Hop count limitation is 255 with the default set at 100

Utilizes the Diffuse Update Algorithm (DUAL) to check the value of the routes

Maintains routes including those that are already-managed by different routingprotocols

Is attuned with the present IGRP implementation

Can route Novell Netware Internetwork Packet Exchange (IPX), Apple Talk,Internet Protocol (IP) and other routed protocols.


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Characteristics of EIGRP

EIGRP is widely-acknowledged as more of a distance vector protocol , but by definition, it is also a hybrid routing protocol because it has advanced featuresusually found only in link-state protocols. Here are the characteristics of theEIGRP:

. EIGRP evaluates the efficiency of the routes by using these metrics:

Default Metrics: Delay and Bandwidth

Optional Metrics: MTU, load, Reliability

Diffusing Update Algorithm: Route efficiency.

2. As with the rest of link-state routing protocols, OSPF and EIGRP direct theupdates about routes only if it detects deviations within the network.

3. EIGRP is only exclusive to Cisco routers.4. EIGRP performs its functions using two main directorial distance figures:

170 – routes from other protocols

90 – routes from EIGRP


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Components of EIGRP

This router protocol comprises four components:

. Protocol-dependent Modules: These are independent modules utilized by specific protocols when sending and receiving data packets within the OSInetwork layer.

. Reliable Transport Protocol (RTP): This protocol guarantees adependable delivery system that transports the EIGRP unicast or multicastdata packets to routers nearby.

. Neighbor Discovery/ Recovery: EIGRP employs a smart system thatdetermines the existence of the nearest routers within the local network.

. Dual finite-state machine: In order to estimate and determine routes thatare free from loops, EIGRP uses a routing algorithm that recognizes a metricthat selects routes based on the feasibility of each routing successors.


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Routing Tables

EIGRP collects data about nearby routers and the landscape of the network andthen stores it to a sequence of tables called routing tables. The three kinds of routing tables used by the EIGRP are:

. Neighbor Table: This stores information using the local network or

computer systems directly connected to each other. The information is thenorganized in a table that contains addressing and interface figures. Each Ciscorouters uses its own EIGRP; hence:

Each router is given a clear map of all the neighbor routers within the samenetwork.

Each router is given an inventory of details of each peer router.

2. Topology Table: This summarizes all network destinations that areroutable through EIGRP and estimations using a metric that detects whether adestination is in an active or passive status. Each Cisco router also runs OPSFto manage a separate link-state table; hence:

Each router has a clear map of network topology not just of its own network but the networks in surrounding network areas of neighbor routers.

Each router gets a deeper understanding of the network topology by using link-state and neighbor table. It gets a clear picture of how the topology within the

router’s and its neighboring router’s surrounding network vicinity work.The topology table manages the following in each of the network destinations:

Successor Route: This is the most efficient route to the destination point asdetermined by DUAL.

Feasible Successor Route: This is the second best route to the destinationpoint, also determined by DUAL.

3. Routing Table: This is a collection of all destination routes mapped down

using the information obtained from all the entries in the topology table. If both the link-state and neighbor tables count the number of available routes,the routing table describes each route.


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EIGRP Packet Types

. ACKs/ Hello: (Unicast) This packet is used when initiating initial discovery or recovery process of neighboring router locations. ACKs are packetscontaining unicast addressed with a specific non-zero numbers exchanged asan acknowledgement receipts between routers.

. Updates: (Unicast) These packets have routing procedures accepted by nearby devices to help create and manage a routing table for the overallnetwork topology.

. Queries: (Multicast) These packets that contain coded queries are sent when adestination point is activated.

. Replies: (Unicast) These packets are sent as a response to the queries sentfrom the origin point.

. Requests: (Unicast, Multicast) These packets are used to obtain pertinentinformation from nearby network devices.


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Convergence

As mentioned earlier EIGRP has faster convergence than that of both IGRP andRIP because routers in the same local network merely exchange ACK packetsinstead of the usually distance vector protocols. With EIGRP, routers becomemore familiar with each other while undergoing the convergence procedure by

exchanging network parameters to each of their neighbor tables.Routers are only considered as “nearby” or “neighboring” routers if thefollowing conditions are satisfied:

Routers have successfully transmitted and received ACK/ Hello packets witheach other.

They have the same independent system that has the same interface withsimilar routing designs.

Each of their ACK/ Hello timer is set to the correct value especially for thefollowing metrics:

a. Network frequency at which each routers exchange ACK/ Hellopackets with each other

b. Farthest distance before the routers consider a router out of coverage network


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Diffusing Update Algorithm (DUAL)

DUAL is a Cisco-proprietary algorithm that assesses each of the routes managed by the EIGRP. This algorithm is responsible for improving the performance of theEIGRP compare to IGRP by circumventing looping routes.

DUAL calculates the successor route and the feasible successor route for the

destination networks.

DUAL allows EIGRP to use routes across different networks using varyingsubnets by means of variable length subnet masking (VLSM)

DUAL provides other feasible successor routes should the best route beunavailable.


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Classful vs. Classless Routing

The two types of routing protocol supported by EIGRP are classful and classlessrouting. If used in their default settings, both the IGRP, RIP (version 1) andEIGRP are all classful routing protocols. By implementing a no auto-summarycommand in the Cisco IOS interface, the router can be configured to support

classless routing. The differences between the two routing protocols are as follows:

Classful Routing Protocol Classless Routing Protocol

When sending route updates,this protocol does not transmitsubnet data.

When sending route updates,this protocol transmits subnetdata.

Based on the class of IP

address, this protocol providesa summary of routes within the boundaries of the network.

This does not provide a

summary of routes within thenetwork unless manually commanded to using the routerinterface.

iscontiguous Networks are networks that have a number of subnets thatcontain varying classes of IP address. They are required when implementing

classless routing protocol.


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Configuring EIGRP

Similar to how RIP is configured in a Cisco router, EIGRP is configured by following these steps:

. Run the EIGRP on each Cisco router

In the IOS interface, run the following code in global configuration mode:router eigrp as_id

The as_id is the routing domain identification otherwise known as the

autonomous system (AS) number. The AS number must be the same for allrouters that will be sharing EIGRP routing information. This number should be within the range of 1 to 65535.

Routing Configuration of the EIGRP (cisco.com)

2. Enable EIGRP

As in the previous step, using the IOS interface run the following code toenable the EIGRP:

Network int_IPThe int_IP in the command is simply the IP address that will identify which interface will support the OSPF in the network.


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Run the following codes when configuring the EIGRP:

For Router 51 -1

R51-1 > en

R51-1 #config t

R51-1(config)#router eigrp 1

R51-1(config-router) #network 192.168.25.2

R51-1(config-router) #network 51.10.0.2

R51-1(config-router) #no auto-summary

R51-1(config-router) #exit

R51-1(config) #exit

R51-1 #disable

R51-1 >

For Router 251:

R2551 > en

R2551 #config t

R2551(config)#router eigrp 1

R2551(config-router) #network 192.168.25.2R2551(config-router) #network 51.10.0.2

R2551(config-router) #no auto-summary

R2551(config-router) #exit

R2551(config) #exit

R2551 #disable

R2551 >


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Managing EIGRP Operation

Using the IOS Interface for Cisco routers, the elements of EIGRP can bemonitored and verified to ensure that the routers are available to determine the best routes.

To take a good look at the routing tables, the following code can be run in the IOS

interface:

show ip route

This command will then display the following information:

Subnets available

Information on the Network Internet Protocol

Routes that are recognized and saved in the routing table

For each route, the interface displays the following data:

Destination network that can be reached by the route as determined by the IPaddress

If the router and the destination network of a route is directly linked to eachother.

The gateway’s IP address if the router is not directly linked to the desireddestination network of a route.


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Other EIGRP-related Terms

Here are other EIGRP terms that you need to commit to memory in preparationfor the CCNA Certification Exams:

. Passive Destination Networks: These are converged networks where boththe best (successor) and second best (feasible successor) routes are converged

in the networks. All routers are aware of these routes without having to shareupdates with each other.

. Active Destination Networks: These networks have not been converged yet. Routers are still on the process of exchanging routing information witcheach other.

. Smooth Round-Trip Timer (SRTT): The amount of time spent by a datapacket to reach the neighboring router and then back to the origin router. This

determines the amount of time routers typically wait for responses from nearby routers.

. Retransmission Timeout (RTO): The value displayed here is the amountof time the router spends before it resends a data packet without notice of receipt from the neighboring router.

. Queue Count (Q Cnt): The value displayed here represents how many datapackets are lined up for sending. Some causes of high Q Cnt values are: (a) toomuch information sent to neighboring routers, (b) neighboring router isoutdated hence not fast enough to receive data, and (c) error in the link between the origin and the destination routers.


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Chapter 5. Open Shortest Path First (OSPF)Protocol

Just like EIGRP, Open Shortest Path First (OSPF) is a link-state routing protocol.Unlike EIGRP however, OSPF is not just supported by Cisco but also by otherrouter manufacturers. When dealing with a wide-scale network environment, theOSPF uses a protocol called IGP short for interior gateway protocol. IGP createsand manages routes only within a singular routing domain.

Already mentioned in the previous chapter, a singular routing domain is simply autonomous system (AS). The AS is simply routers and network addressesgrouped together that are within the same routing network system. It can be

inferred then that any network that has OSPF integrated in all the connectedrouters is operating under the AS.

Another example of an autonomous system is the Intermediate System-to-ntermediate System (IS-IS) routing protocol. This routing protocol is used for

large networks like that of an internet service provider. The Border Gateway Protocol (BGP) is another good example of an autonomous system. The BGP ismeant to link other autonomous system and large networks managed by internetservice providers.

OSPF Routing Tables

Similar to the EIGRP, OSPF manages a neighbor table and a routing table. Theonly difference is that EIGRP has a topology table whereas the OSPF has a link-state table.

Link-State Table: This table manages the connections between the routerand neighboring router by measuring the stability of each of theseconnections. Simply, it observes the quality of routes to neighboring routers.


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Characteristics of OSPF

. As in EIGRP, route updates are only transmitted when OSPF has detected any change in the routes.

. When the OSPF does detect changes, the router automatically transmits a link-state advertisement (LSA) in one of the routes whose properties are stored inthe routing table. Only information about the changes in one of the routes iscontained in the LSA.

LSA packets leave almost no network footprint or trace.

LSA traffic is kept at a minimum because OSPF keeps an inventory of routes.

LSA traffic is organized in such a way that LSA packets reach the destinationrouter immediately.

3. Routers shares CKA/ Hello messages with each other as they establish the values in each of their neighbor tables while undergoing the convergenceprocess.

4. Unlike EIGRP, which is a Cisco-proprietary protocol, OSPF is supported by other router manufacturers.

5. OSPF converges fast compared to other protocols (except EIGRP).

6. OSPF works efficiently because it divides the system (routing domain) into

different sectors of control.7. Limitless amount of network hops are supported by the OSPF.

8. Variable-length subnet masking (VLSM) is supported by the OSPF.

9. OSPF organizes and reads routers in a hierarchical format.


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Convergence

During the convergence process, the routers exchange pleasantries by sharingnetwork parameters before storing received data to each of their neighbor table.There is no need to discuss in great detail how routers recognize each other asneighbors since convergence in OSPF is exactly the same with convergence in

EIGRP.


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Cost Metric

To measure the value of the connections established by each route, the OSPFemploys a cost metric.

Route cost is a metric that determines the value of each connection by its bandwidth. By dividing the default 100Mbps or roughly, a million bits per second)

bandwidth with the measured bandwidth of the connection.

For example, if the router measured the actual bandwidth as:

10 Gbps

(10,000,000,000 bps)

100,000,000 bps

10,000,000,000 bps

0.01

1 Gbps

(1,000,000,000 bps)

100,000,000 bps

1,000,000,000 bps

0.1

100 Mbps

(100,000,000 bps)

100,000,000 bps

100,000,000 bps

1

10 Mbps

(10,000,000 bps)

100,000,000 bps

10,000,000 bps

10

1 Mbps

(10,000,000 bps)

100,000,000 bps

1,000,000 bps

100

The faster the bandwidth of the connection, the lower the route cost. OSPF isdesigned to compute for least cost and use it for sending packets.

In the above example, the default reference bandwidth is pegged at 100 Mbps butusing the Cisco IOS interface, you can change this reference value by using thiscode:

auto-cost reference bandwidthThis is handy when using high-powered machines that transmit data packets inhigh-speeds. Instead of using 100 Mbps as reference, you can set it to 10 Gbps by


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implementing the following command codes:

RT51-2> en

RT51-2 #config t

RT51-2(config) #auto-cost reference-bandwidth10000000000

RT51-2(config) #exit

RT51-2 #disable

RT51-2>


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OSPF Hierarchy

The OSPF employs a special routing algorithm that determines the shortest path between the origin point (router) and the destination point (neighbor router). Thisspecial algorithm is called the Djikstra routing algorithm.

The Djikstra algorithm in a router sees the origin router as a root router. The

algorithm assigns areas where there is at a single designated router (DR). Ideally however, a backup designated router (BDR) is also assigned.

Photo: OSPF Credit: routerprotocol.net

Refer to the figure on the left. Since DR-10 Router is nearer vis-à-vis other routers,it is designated as the designated router for Area 10. The same can be said for DR-20 router, which is the designated router for Area 20. In other words, if the rootrouter intends to send a data packet to Router 10-1, it will first assess if the shorterroute (DR-10) is available. If it is, then it sends the data packet through DR-10 en

route to DR 10-1.


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Selecting a Designated Router (DR)

The computations made by the OSPF priority algorithm determine the designatedrouter. The algorithm produces a value within the range of 0 ANS 225 isintegrated to the IOS interface by running:

ipospf priority value

The default value of the OSPF is 1. The router assigned with the highest OSPFpriority value becomes the designated router. In the remote instance that tworouters are assigned with the same OPSF priority value, the tie will be broken by using the router ID (RID).

Using the following methods, users can choose which router should be assigned asa designated router by:

OSPF Priority: Set the highest priority value for both the interface and the

router.

Lookback Interfaces: In each router, the user can create an effective lookback interface and set the highest IP address to one of the routers intended to bedesignated router.


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Router ID (RID)

This is the IP address generated to serve as an identifier of the router. It is set by employing the following methods:

Using the command router-id in the Cisco IOS interface

Manually by:

Assigning a high IP address to the router’s loopback interface

Assigning a high IP address in the router’s active interface


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Configuring the OSPF

The steps to configure the OSPF on any Cisco Routers are very similar to how bothEIGRP and RIP can be configured. It is accomplished by:

. Starting up the OSPF

In the global configuration mode, this command can be run in the Cisco IOSinterface:

router ospf pro_id

The variable pro_id is assigned a number within the range of 1 and 65536.

This number serves as an identifier of the protocol’s routing process thatexchanges information with other routers through the OSPF.

2. Enable OSPF on the interface

Using the Cisco IOS interface, OSPF is enabled by implementing thiscommand code:

network idt_IP IP_mask area area_idt

idt_IP This assigns the IP address that willserve as the main identifier of thesystem interface where OSPF will beenabled.

IP_mask This portion determines which of theIP addresses listed on the neighboringtables belong to the network.

areaarea_idt

This defines the extent by with theOSPF can operate.

The IP mask or wildcard mask are in essence simply bit masks. A bit mask is a

combination of numbers 1 or 0 and is hence, following the binary system. In theOSPF, bit masks have the following significance:

1 Any number can be assigned to thematching bit in the IP address.

0 Exact number should be the same as thatof the matching bit in the IP address.

Consider the IP address in its entirety. It is divided into four numbers or into 4 bytes with each byte containing 8 bits. The wildcards can be set as any number within the range of 0.0.0.0 and 255.255.255.255. These decimal numbers have thefollowing significance:


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255 Any number can be assigned to thematching bit in the IP address. Whenconverted to the binary system, 255 isequivalent to a series of eight 0s.

0 Exact number should be the same as that

of the matching bit in the IP address. When converted to the binary system,255 is equivalent to a series of eight 1s.

If let’s say the command code implemented in the Cisco IOS interface begins withthe following IP address combination: 192.167.25.0 0.0.0.0 then only routers withIP address 192.167.25.0 are exposed. If, however, the IP address combination is192.167.25.0 – 0.0.0.255 then all the routers that begin with 192.167.25 as an IP

address will be exposed.Here is the corresponding IP address for each of the Cisco router:

Router 10-1 172.10.78.0

Router 10-2 172.10.77.0

Router DR-10 172.10.75.0

Router BDR-10 172.10.76.0

Consider the following command configuration for Router 10-1:

R10-1 >en

R10-1 #config t

R10-1 (config) #router ospf 1

R10-1 (config-router) #network 172.10.78.0 0.0.0.255area 20

R10-1 (config-router) #network 172.10.78.0 0.0.15.255area 10

R10-1 (config-router) #exit

R10-1 (config) #exit

R10-1 #disable

R10-1 >

The above command configuration of router 10-1 affects the interface for botharea 20 and area 10 by:


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Area 20 Router 10-1 exposes to all routers withinarea 20 any routers assigned with the IPspace 172.10.78 within the network with thesame IP address 172.10.78

Area 10 Router 10-1 exposes to all routers within

area 10 any routers whose IP begins with172.10.7 only. Simply, the IP address can be172.10.75 to 172.10.78.


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Pertinent Commands

When reviewing for the CCNA certification, you will find the following commands(not already mentioned in the previous section of this chapter) handy:

show ip ospf

interface

This is used to inspect the

current IP configuration of theOSPF protocol.

If the command isimplemented in a specificinterface, the interface willonly display informationpertaining to the saidinterface.

If this is not the case, thenthe command will display acomprehensive list of information pertaining toeach interface powered by OSPF.

ip ospf neighbor This displays information about

OSPF information of neighborrouters.

show ip ospfdatabase

This inspects the data held by the routing tables of the OSPFprotocol. The command notonly displays information aboutrouters within the samenetwork, it also displays the

status of each connection fromthe root router.

debug ip ospf This command code is use totroubleshoot any noticeablerouting malfunctions.

no debug ip ospf This command disables thedebugging capabilities of OSPF.


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Part 2Switching with CISCO Switches


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Chapter 6. Layer 2 Switches

If Layer 3 is the network layer, were routers transmit data packets to other

routers, Layer 2 is the data link layer in networks that follow the TCP/IP or OpenSystems Interconnection (OSI) model.

Layer 2 is responsible for sending data to physical devices. Each device is assigned with its own physical address recognized by the network to route data packetsfrom one device to another. Otherwise called as Media Access Control (MAC)addresses, the physical addresses act as a unique identifier to specific network devices.

The features of the data link layer are as follows:

1. Communicates with the network layer to liaise the receipt of data packets fromthe source host

2. Assembles the received packets inside a data frame with the MAC address(local routing information).

3. Transmits the packaged data frame to the physical layer, which will then break down the code to specific optical and electrical signal.

The physical layer (comprised mainly by the physical device) transmits the codesinside the data frame through wired connection or wireless sending.

Within the receiving module, Layer 2 initiates the following:

1. Opens the data frame

2. Acquires the data packet from the data frame

3. Transmits the data packet to the network layer

For data link procedures, the TCP/IP (Ethernet) protocol is used at the data link

layer. According to the standards prescribed by the IEEE802.X, the Ethernetmanages the TCP/IP operations in Layer 2.

The main role of the data link layer is to manage the transmission of data frameslocally between two physical devices bound together by the Local Access Network (LAN).

For a better understanding about how Layer 2 switches work, consider thefollowing:

Earlier LAN implementations used a coaxial cable to connect computerstogether.

The bandwidth is spread and shared within the different devices connected to


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the LAN.

Due to the shared bandwidth, all data packets are shared to all devicesconnected to the LAN instead.

For example, there are four computer users — Matt, Mark, Joe, and Lucas —connected to a network. If a data packet is sent to Matt, the other users see the

packet too. Not only does this undermine privacy of the content of said packet,Mark, Joe and Lucas need to delete the data packet because it is not addressed tothem. Every time at least one of them receives a data packet, the rest would haveto delete the packet on a regular basis. Not only is this bothersome; it is alsoinefficient.


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Hubs

Having realized this problem, hubs were later introduced to integrate computerdevices together using a single cable per device. Instead of coaxial cables,computer hubs use twisted-pair cables. RJ-45 connectors are used at end of cablesto simplify connection.

RJ45 ( rj-group.com )

When data frames are sent to a hub, they are transmitted to all host computersconnected to the hub with the exception of the source device. Simply, the

mechanism of the hub sends the data to all inbound ports except from where thedata frame originated.

Since the data frames are being sent to different inbound ports while at the sametime share the same bandwidth, there is a high possibility for data frames tocollide. To completely devoid the network hub of data frame collisions, theEthernet employs a special mechanism called Carrier Sense Multiple AccessCollision Detect (CSMA/CD).

The CSMA/CF uses an algorithm that manages the transmission of data packets tothe rest of the connected devices so that none of the transmitted packets willcollide. This, however, consumes almost half of the bandwidth that could have been used for faster data transmission.


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Hub (cisco.com)

The only way to circumvent the problem is to make the collision domain as littleas possible. This is where Layer 2 bridges and switches come in.

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